Astrophysicist speeds up radioactive decay

A German physicist thinks he may have found a way to accelerate the process of nuclear decay, dramatically shortening the half life of dangerous nuclear waste.

Claus Rolfs, chair of experimental physics at Ruhr University, and his team suggest that embedding an alpha emitter in metal and cooling it to just a few degrees Kelvin could reduce its half life to perhaps just tens of years, instead of thousands. If he is right, the whole business of burying nuclear waste in concrete bunkers could be neatly side-stepped.

However, critics say his idea doesn't hold up, that it contradicts existing theory as well as other experimental results. Nick Stone, a retired nuclear physicist from Oxford University, told Physics Web that experiments with cooled, metal embedded alpha emitters had already been run by other physicists, and that no reduction in half life had been observed.

Rolfs, however, is determined that his work is good, although he acknowledges that the theory needs refining.

Rolfs is an astrophysicist, and was working on reproducing stellar fusion when he noticed something odd about alpha decay. He saw that the rate of fusion reactions in his particle accelerator was higher when the target nuclei were encased in metal. Cooling the metal sped the reaction rate even further.

This, he says, gave him the idea.

He proposed that the phenomenon could be explained using a model that assumes free electrons in a metal behave as though they are in a plasma. As the metal cools, the electrons get closer to the nuclei. This encourages positively charged particles in towards the nuclei, making it more likely that one of them will hit and spark a fusion reaction.

Rolfs reasoned that same process might also hasten the ejection of a positively charged particle, such as an alpha particle, from the nucleus, and slow the ejection of electrons from the nucleus. If it did, one could expected shorter half lives for alpha decay, and longer half lives for negative beta decay, or electron capture.

Initial experimental results seem to support the theory. Cooled, metal-embedded beryllium-7's electron capture had a longer half life, while the half lives of positive beta decay of sodium-22 and alpha decay of polonium-210 were shorter. Radium-226, a by-product of nuclear power plants, is next on the list for testing.

Hubert Flocard, director of the CSNSM nuclear-physics lab near Paris told PhysicsWeb that although he can't explain the results, Rolfs' work contradicts the standard model of solid state physics.

It remains to be seen whether this means it is Rolfs' theory, or the standard model needs rejigging. ®